Drive controls are used in the field of automated system technology for controlling movement sequences in machines, in particular machine tools, production systems and robot arms. Their operating principle consists of converting movement setpoint values into actuating signals for motors, to measure, as actual values, the movement induced by the motors by position measuring devices, and to adapt the actuating signals such that setpoint and actual values match as closely as possible.
Position measuring devices which supply an absolute position value are becoming more prevalent in such drive controls. This does away with certain disadvantages of so-called incremental position measuring devices, such as the need to perform a reference execution following the activation, in order to find a reference position which serves as reference point for the further position measurement by counting graduation marks.
The transmission of absolute position values is mainly implemented with the aid of serial data interfaces because these interfaces require only a few data transmission lines and provide high data transmission rates nevertheless. A multitude of standard interfaces has come to dominate in the field of automation technology. Popular representatives of serial interfaces for position measuring devices are, for example, the EnDat interface and the SSI interface. The basis of the EnDat interface is described in European Patent No. 0 660 209, and the function of the SSI interface is described in European Patent No. 0 171 579.
Because the movement sequences of machines are ultimately determined by position values generated in absolute position measuring devices and digitally transmitted to the drive control via serial interfaces, it is of the utmost importance for the safe operation of a machine that errors in the generation and transmission of the position values are avoided. In the event that an error has occurred nevertheless, it is also important that such an error is highly likely to be discovered before it can affect a movement sequence. Otherwise, even a single incorrectly generated and transmitted bit in a position value may cause an uncontrollable, unforeseeable and jerky motion of the machine. In addition to considerable damage to the machine, life-threatening situations for the operating personnel present in the operating area of the machine may arise as well. As a result, the detection of faulty position values is given the highest priority in the field of automation technology.